According to Russia, Israeli F-16s flew in low under the Il-20 to either shield themselves from air defense fire or make Syrian air defenses, which use outdated technology, shoot down the bigger, easier to spot Il-20 rather than the sleeker F-16s.

Whether or not Israel purposefully used the Il-20 to its advantage remains an open question. But it exposed a glaring flaw in Syrian and Russian military cooperation, which Moscow is due to close with the S-300.

Russians hit the front lines, and Israel won't back off

An S-300 air defense missile system launches a missile during the Keys to the Sky competition at the International Army Games 2017 at the Ashuluk shooting range outside Astrakhan, Russia August 5, 2017. Reuters

According to Nikolai Sokov, a Senior Fellow at the Middlebury Institute of International Studies at Monterrey, the Russians will now sit on-site at Syrian air defense sites, which Israel frequently bombs.

Syria's current air defenses lack the highly-classified signal Russian planes send to their own air defenses to identify them as friendly. Without this secret sign from the flying Il-20, Syria mistook it for an enemy, and shot it down.

If Russia could simply give Syria the signal and fix the problem, it would have likely done so already. But if Syria somehow leaked the signal, the US or NATO could trick all Russian air defenses into their fighters were friendly Russian jets, leaving Russia open to attack, according to Sokov.

"The S-300 systems Russia plans to supply to Syria will feature a compromise solution," said Sokov. "They will be fully equipped to distinguish Russian aircraft... but there will be Russian personnel present at controls."

Israel has admitted to more than 200 air strikes within Syria in the last two years. These strikes have killed more than 100 Iranian fighters in Syria in the last month alone, the Syrian Observatory for Human Rights reports.

Frequently, Syria responds to these strikes with air defense fire against Israeli fighter jets. In February, Syria succeeded in downing an Israeli F-16. Israel responded with a sweeping attack it claimed knocked out half of Syria's air defenses.

Trends point to a big fight

Israeli security forces examine the remains of an F-16 Israeli war plane near the Israeli village of Harduf, Israel February 10, 2018. REUTERS/Ronen Zvulun

Iran has pledged to wipe Israel off the map, and has for decades tried to achieve that by transferring weapons across the Middle East to Israel's neighbors, like Lebanon where Hezbollah holds power.

In short, Israeli strikes that require air defense suppression (such as blowing up Russian-made air defenses in Syria) will not stop any time soon, judging by Israel and Iran's ongoing positions.

But now, when Israel knocks down a Syrian air defense site, it runs the risk of killing Russian servicemen. When Israel kills Syrians, Syria complains and may fire some missiles back, but its military is too weak and distracted by a seven-year-long civil war to do much about it.

If Israel kills Russians, then Russia's large navy and aviation presence could mobilize very quickly against Israel, which has fierce defenses of its own.

"Obviously, this seriously constrains not just Israeli, but also US operations in case of possible bombing of Syria," Sokov said of the new Russian-staffed S-300.

"Not only Syrian air defense will become more capable, but it will be necessary to keep in mind the presence of Russian operators at the Syrian air defense systems."

So next time Israel or the US decides to strike Syria, it may not only find stiffer-than-usual resistance, it might find itself in a quickly escalating battle with one of the world's greatest military powers.